Motor having gear for transmitting torque and substrate with cut-out section between coils

ABSTRACT

A motor comprising a rotor unit and a stator unit. The rotor unit includes a multipolar rotor magnet; a gear, disposed away from the center of rotation of the rotor unit with respect to the rotor magnet, for transmitting torque of the rotor unit to the outside; and a rotary shaft disposed at the center of rotation. The stator unit includes a substrate; and a plurality of coils disposed facing the rotor magnet on the substrate, the substrate having a cut-out section between at least two of the plurality of coils, with the cut-out section causing the outer peripheral section of the gear to be exposed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motor suitable for use as a capstanmotor for performing tape drive in a video tape recorder (hereinafterreferred to as "VTR").

2. Description of the Related Art

A conventional VTR is provided with a capstan motor for driving andtransporting a tape, like recording medium, along with a pinch roller,and a reel motor for winding up the transported tape. In addition, theVTR is provided with a tape guide disposed in place for winding theaforementioned tape around a cylinder, and a loading motor for drawingout the tape from a cassette, with a cylinder motor provided for theaforementioned cylinder for driving and rotating a magnetic head.

In recent years, however, to produce a smaller and cheaper videocamera-VTR combination (camcorder) with low power consumption, tapewinding by the aforementioned reel motor has been primarily performed bytransmission of driving power from the capstan motor.

In particular, in recent years, to respond to the demand for smaller andthinner VTR mechanisms, a system has been disclosed, for example, inJapanese Patent Utility Model Laid-Open No. 1-109275 in which a gear isformed at the outer periphery of a rotor unit integrally with a rotormagnet to obtain driving power from a side face thereof. This system issuitable for producing thin and smaller VTR mechanisms because thedriving power is extracted from a side of a capstan motor section via atransmission gear.

As illustrated in FIG. 6, which is a perspective view of an appearanceof this type of capstan motor, in the conventional system in whichdriving power is extracted via a transmission gear formed at the outerperiphery of the rotor unit, it is necessary, for assembly purposes, tocut out a portion of a stator (yoke) 1 where the transmission gear 8(through which driving power is extracted) engages with an outerperipheral gear 14. The cut-out section is denoted by reference numeral1a.

Therefore, as in FIG. 7, which illustrates a stator unit of the motor,the driving power generating section, in particular the outer peripheralradius R₂ of each of the six driving coils 17, is very small compared tothe outer periphery of the motor, making it necessary to maintain therequired motor characteristics by making the motor thicker, making thedriving magnet more magnetic, etc.

Referring to FIGS. 6 and 7, reference numeral 3 denotes a wiringconnector to a motor drive circuit (not shown), reference numeral 5denotes a bearing metal, reference numeral 6 denotes a bearing housing,reference numeral 7 denotes a magnetic resistance (MR) element,reference numeral 9 denotes a holder, reference numeral 14 denotes anouter periphery gear, reference numeral 15 denotes a grease retainer,reference numeral 16 denotes a capstan shaft, and reference numeral 18denotes a Hall device.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a motorstructure which allows a motor torque generating section of sufficientsize to be used even when a cut-out section is required in the statorunit substrate (stator yoke) for motor assembly purposes.

To this end, there is provided according to one aspect of the presentinvention a motor including a rotor unit and a stator unit. The rotorunit includes a multipolar rotor magnet; a gear, disposed away from thecenter of rotation of the rotor unit with respect to the rotor magnet,for transmitting torque of the rotor unit to the outside; and a rotaryshaft disposed at the center of rotation. The stator unit includes asubstrate, and a plurality of coils disposed facing the rotor magnet onthe substrate, the substrate having a cut-out section between at leasttwo of the plurality of coils, with the cut-out section causing theouter peripheral section of the gear to be exposed.

According to another aspect of the present invention, there is providedan electronic apparatus comprising a motor and a transmission gear. Themotor includes a rotor unit and a stator unit. The rotor unit includes amultipolar rotator magnet; a gear, disposed away from the center ofrotation of the rotor unit with respect to the rotor magnet, fortransmitting torque of the rotor unit, and a rotary shaft disposed atthe center of rotation. The stator unit includes a substrate, and aplurality of coils disposed facing the rotor magnet on the substrate,the substrate having a cut-out section between at least two of theplurality of coils, with the cut-out section causing the outerperipheral section of the gear to be exposed. The transmission gear isarranged to engage with the gear.

Other objects and features of the present invention will become apparentin the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is illustrative of a stator unit of a capstan motor of anembodiment of the present invention.

FIG. 2 is a sectional view of the capstan motor of the embodiment ofFIG. 1, with the motor being cut at the center along line 2--2 .

FIG. 3 is illustrative of a driving coil of the embodiment of thecapstan motor of FIG. 1.

FIG. 4 is illustrative of a driving coil of a conventional capstan motorillustrated in FIGS. 6 and 7.

FIG. 5 is illustrative of a stator unit of an embodiment which is animprovement over the aforementioned embodiment.

FIG. 6 is a perspective view of an appearance of a conventional capstanmotor.

FIG. 7 is illustrative of the stator unit of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given of an embodiment applied to a VTRcapstan motor with reference to the drawings.

FIG. 1 is illustrative of the stator unit of the capstan motor of anembodiment of the present invention which corresponds to the stator unitof FIG. 7 and is composed of an iron substrate having a pattern formedon an iron plate which has driving coils placed thereon. FIG. 2 is across sectional view of the capstan motor cut at the center along line2--2. Although not illustrated, the recording medium or tape istransported as it is passed in contact between a capstan shaft 16 and apinch roller (not shown) disposed facing the capstan shaft 16 of thecapstan motor.

Referring to FIGS. 1 and 2, reference numeral 1 denotes a statorsubstrate (yoke) which is an iron substrate having an insulation layerformed, for example, on an iron plate or silicon steel plate, a copperfoil formed on the insulation layer, and a pattern formed by etching.Three driving coils 2 are disposed along the circumference atpredetermined phase angles θ_(c). Reference numeral 3 denotes a flexibleprinted board connector for wiring to a motor driving circuit (notillustrated).

Reference numeral 4 denotes Hall devices, which are disposed atpredetermined phase angles θ_(H), for detecting the rotational phase ofa driving rotor magnet. Reference numeral 5 denotes a bearing metal forsupporting a capstan shaft 16, while reference numeral 6 denotes abearing housing for holding the bearing metal.

Reference numeral 7 denotes a magnetic resistance element (hereinafterreferred to as "MR element"), which is disposed at the outer peripheryat the rotor side, for detecting the rotation period based on themagnetic flux and magnetic field of the plastic rotor magnet magnetizedin a predetermined manner at a pitch of less than 0.5 mm along the outerperiphery. Reference numeral 7a denotes a lead terminal of the MRelement 7. Reference numeral 8 denotes a transmission gear engaging anouter peripheral gear 14, which is disposed along the outer peripheryadjacent to the rotor. Reference numeral 1a denotes a cut-out sectionformed so that the stator yoke 1 does not get in the way when thetransmission gear 8 is being assembled. The radius of the outerperipheral gear 14 is smaller than radius R1 (FIG. 3) of each coil 2 tobe discussed later. This is apparent from linking section 8a of the gear8 of FIG. 1.

When, for example, the driving rotor magnet 13 (of FIG. 2) has 8 poles,the phase angles θ_(C) at which the driving coils 2 are arranged are inthe range of from θ_(C) =45°+15°×(3n-) to θ_(C) =45°+15°×(3n -2).

In FIG. 1, each phase angle θ_(c) is 105°. Each of the three coils 2must be disposed at a phase angle θ_(C) greater than 60° to avoid thecut-out section 1a . Therefore, at least two of the phase angles θ_(C)must be greater than 60°.

Although the phase angles θ_(H) of the Hall devices 4 can be in the samerange as the phase angles of the coils 2, they are determined by θ_(H)=15°+45°n. This is because each Hall device 4 output needs to have anelectrical angle phase difference of 30° with respect to the coil 2.

FIG. 3 is a plan view of the shape of each driving coil 2, while FIG. 4illustrates the shape of each driving coil 17 of the conventional motorstructure shown in FIG. 7, the illustration given for comparison.Comparing the two figures, the outer peripheral radius of each coil, R₁,is greater than the outer peripheral radius of each coil, R₂, with eachopen angle θ_(K1) being less than each open angle θ_(K2).

The shape of each driving coil 2 of the embodiment is such that theinner open angle θ_(K1) of each fan-shaped coil is smaller than theangle of magnetization of the driving rotor magnet 13, so that when thenumber of windings of each coil 2 is increased, the portion along thecircumferential dimension that does not cause generation of torque ofthe motor can be made shorter, thereby preventing an increase in theresistance value.

In the embodiment, the angle of magnetization is 45° when there areeight poles, with the open angle θ_(K1) being 45°. In the conventionalexample the open angle θ_(K2) is 45° to 60°, which is larger than theangle of magnetization. When it is 60 to 90% of the magnetic pole angle,lowered efficiency caused by a phase difference between the torquegeneration direction and the rotation direction occurs rarely, so thatit can be kept down to a range of about 2% or less.

In the conventional example, it is necessary to form a cut-out section1a in the stator yoke 1 for allowing linkage with the transmission gear8, so that the outermost peripheral radius R₂ (of FIG. 4) is limitedwith respect to the motor size. In this embodiment, however, since thenumber of coils is halved, there is more space between the coils, thisextra space being used for linking the gear. This makes it possible tomake the outer peripheral radius of the coil arrangement to be large asR₁ of FIG. 3.

It is possible to reduce the number of coils and increase the outerperipheral radius of the motor, so that narrowing the open angle of eachcoil 2 and increasing the number of windings makes it possible toproduce a better motor providing sufficient torque.

FIG. 2 is a cross sectional view of the capstan motor of the firstembodiment of FIG. 1, with the motor cut at the center along line 2--2 .With respect to the stator unit described in FIG. 1, the plastic rotormagnet 13 is disposed facing each driving coil 2 and secured to thecapstan shaft 16 through the rotor yoke 12 and a bushing 11.

The outer peripheral gear 14 is secured to the outer periphery of therotor yoke 12. The gear 14 is formed by the plastic rotor magnet 13having a gear portion engaging with a transmission gear 8.

A bearing metal 5, which supports the capstan shaft 16, is secured tothe bearing housing 6. The suction force between the stator substrate 1and the rotor magnet 13 is received by a thrust receiver 10 and held.

FIG. 5 is illustrative of an embodiment which is a partial improvementover the aforementioned embodiment. In this embodiment, the MR elementterminals 7a is disposed at the inner side of the motor.

The conventional MR element 7 is formed by a magnetic resistance filmmade of Ni alloy formed on a glass plate or a ceramic plate, and haslead terminals 7a soldered and extended out and connected on the statorsubstrate 1.

In the FIG. 7 way of connection, the lead terminals protrude out awayfrom the motor, which enlarges only this portion of the motor, so as toresult in a problem regarding where the MR element 7 is to be disposedwith respect to the mechanical system.

In this embodiment, which is an improvement over the aforementionedembodiment, fewer driving coils 2 allows the MR element 7 to be disposedbetween coils as well as the lead terminals 7a to be placed on the motorside for connection. In such a construction, the lead terminal sections7a only protrude out by an insignificant amount from the outer diameterof the motor, making it possible to reduce the size of the mechanicalsystem.

As will be understood from the foregoing description, according to theembodiments, the phases of the gear linking section and the drivingcoils do not overlap, so that a reduction in the number of driving coilsallows larger coils to be used, motor characteristics to be improved,and to provide a cheaper motor.

Making the open angle of the inner side of the aforementioned drivingcoil shape less than the magnetic pole angle makes it possible to reducethe length of the winding along the circumferential dimension to providea highly efficient and cheap motor whose resistance does not increaseeven if a greater number of windings is used.

The lead terminals of the magnetic resistance element do not overlap thedriving coils, which allows the lead terminals to be disposed facing themotor, thereby making it possible to reduce the size of the motor.

The individual components shown in outline or designated by blocks inthe Drawings are well-known in the electric motor arts, and theirspecific construction and operation or best mode for carrying out theinvention.

While the present invention has been described with respect to what arepresently considered to be the preferred embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. To the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. The scope of the following claims is to beaccorded the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

What is claimed is:
 1. A motor comprising:a rotor unit including (i) amultipolar rotor magnet, (ii) a gear, disposed away from the center ofrotation of said rotor unit with respect to said rotor magnet, fortransmitting torque of the rotor unit, and (iii) a rotary shaft disposedat said center of rotation; and a stator unit including (i) a substrate,and (ii) a plurality of coils disposed on said substrate facing saidrotor magnet, said substrate having a cut-out section between at leasttwo of said plurality of coils, with said cut-out section causing theouter peripheral section of said gear to be exposed at a radius from thecenter of rotation less than an outer radius of said plurality of coils.2. A motor according to claim 1, wherein said coils are wound aroundfan-shaped openings, with the angles of said openings being 60 to 90% anangle of magnetization of said rotor magnet.
 3. A motor according toclaim 1 further comprising a sensor for detecting the rotational phaseof said rotor magnet, said sensor being disposed on said substrate andbetween said coils.
 4. A motor according to claim 1 further comprising asensor for detecting the rotation period of said rotor unit, said sensorbeing disposed on said substrate and between said coils, with leadterminals of said second sensor being positioned towards said coils. 5.A motor according to claim 1, wherein the number of said coils is three.6. A motor according to claim 1, wherein said rotary shaft comprises acapstan.
 7. An electronic apparatus comprising: (a) a motor including:arotor unit including (i) a multipolar rotor magnet, (ii) a gear,disposed away from the center of rotation of said rotor unit withrespect to said rotor magnet, for transmitting torque of said rotorunit, and (iii) a rotary shaft disposed at said center of rotation; anda stator unit including (i) a substrate, and (ii) a plurality of coilsdisposed facing said rotor magnet on said substrate, said substratehaving a cut-out section between at least two of said plurality ofcoils, with said cut-out section causing the outer peripheral section ofsaid gear to be exposed at a radius from the center of rotation lessthan an outer radius of said plurality of coils; and (b) a transmissiongear arranged to engage with said gear.
 8. An apparatus according toclaim 7, wherein said coils are wound near fan-shaped openings, with theangles of said openings being 60 to 90% of an angle of magnetization ofsaid rotor magnet.
 9. An apparatus according to claim 7 furthercomprising a sensor for detecting the rotational phase of said rotormagnet, said sensor being disposed on said substrate and between saidcoils.
 10. An apparatus according to claim 7 further comprising a sensorfor detecting the rotation period of said rotor unit, said sensor beingdisposed on said substrate and between said coils, with lead terminalsof said second sensor being positioned towards said coils.
 11. Anapparatus according to claim 7, wherein the number of said coils isthree.
 12. An apparatus according to claim 7, wherein said rotary shaftcomprises a capstan.
 13. A motor comprising:a rotor unit including (i) amultipolar rotor magnet, (ii) a gear, disposed away from the center ofrotation of said rotor unit with respect to said rotor magnet, fortransmitting torque of the rotor unit, and (iii) a rotary shaft disposedat the center of rotation; and a stator unit including (i) a substrate,and (ii) a plurality of coils disposed on said substrate facing saidrotor magnet, said substrate having a cut-out section between at leasttwo of said plurality of coils, wherein said gear and said cut-outsection are configured so that the outer peripheral section of said gearis exposed, and wherein a radius of said gear from the center ofrotation is smaller than a radius of said plurality of coils, andwherein phases of a linking area between said gear and a transmissiongear linked with said gear and of said plurality of coils do notoverlap.
 14. A motor according to claim 13, wherein said coils are woundaround fan-shaped openings, with the angles of said openings being 60 to90% of an angle of magnetization of said rotor magnet.
 15. An apparatuscomprising:a motor comprising (a) a rotor unit including (i) amultipolar rotor magnet, (ii) a rotor gear, disposed away from thecenter of rotation of said rotor unit with respect to said rotor magnet,for transmitting torque of the rotor unit, and (iii) a rotary shaftdisposed at the center of rotation, and (b) a stator unit including (i)a substrate, and (ii) a plurality of coils disposed on said substratefacing said rotor magnet, said substrate having a cut-out sectionbetween at least two of said plurality of coils; and a transmission geararranged to engage with said rotor gear, wherein said rotor gear andsaid cut-out section are configured so that the outer peripheral sectionof said rotor gear is exposed, and wherein a radius of said rotor gearfrom the center of rotation is smaller than a radius of said pluralityof coils, and wherein phases of a linking area between said rotor gearand said transmission gear and of said plurality of coils do notoverlap.
 16. An apparatus according to claim 15, wherein saidtransmission gear and said rotor gear are configured to engage at aradius which is smaller than a radius of said plurality of coils.
 17. Anapparatus according to claim 15, wherein said coils are wound aroundfan-shaped openings, with the angles of said openings being 60 to 90% ofan angle of magnetization of said rotor magnet.